| 摘要 |
PURPOSE:To make constant the degree of light modulation of a diode in a drive circuit having a laser diode, a photodetector, a light waveguide, a negative feedback control circuit for controlling a DC bias current by feeding back an electric signal outputted from the photodetector to the modulation signal input side of the diode. CONSTITUTION:A diode drive circuit has a photodetector 2, a peak detector 17 for detecting the peak value of a received modulation signal, a differential amplifier 18 for amplifying the difference between the output signal of the detector and a reference voltage applied to a negative input terminal 19, and a variable gain amplifier 20 for varying the gain in response to the output voltage of the amplifier 18. With this configuration, light is received by the photodetector 2, the modulation signal monitored by a resistor 15 is applied to the detector 17, and the peak value is outputted to the positive terminal of the amplifier 18. Subsequently, the output of the amplifier 18 is compared with the reference voltage applied to the terminal 19, the difference voltage is applied as a gain control voltage to the amplifier 20, the gain is varied corresponding to the control voltage, thereby varying the amplitude of the modulation signal applied to the laser diode. |
